1. Field of the Invention
The present invention relates to a method of producing ceramic parts, particularly to a suitable method of economically producing ceramic parts of complicated configurations which hitherto can not be produced directly to their final configurations using injection molding process.
2. Description of the Prior Art
Recently, ceramic parts made of a material with superior high temperature characteristics, such as Si.sub.3 N.sub.4, SiC or the like, having increasing application fields in high temperature structural materials by virtue of their superior high temperature strength, heat resistance, thermal shock properties and corrosion resistant properties, and have shown remarkable technical progress.
Ceramic parts of complicated configurations with thin blade portions and comparatively thick axis portion, such as turbo charger rotors for Diesel engines, radial type turbine rotors for gas turbine engines, and the like, are required to have strict dimensional precision as well as superior mechanical and thermal characteristics.
Heretofore, for producing such ceramic parts as the abovementioned rotors of complicated configurations consisting of two portions of different thicknesses, there have been attempted such methods as slip casting and injection molding, etc. using superior heat-resistant Si.sub.3 N.sub.4 SiC powder. However, the slip casting method has a drawback in that it could not produce distal ends of blades portion of such rotors with sufficient precision of shape and dimension, which distal ends have a great influence on efficiency of the rotors. The heretofore used injection molding method has a drawback in that it could not produce directly an integrally molded part of final shape having a thin blade portions of a complicated configuration and a thick columnar axis portion, since a die for filling the molding material sufficiently into its cavity is hardly fabricated. Therefore, in conventional injection molding methods, the ceramic part is produced at first by molding a green body using a material powder and a resin as a molding additive, removing (degreasing) the resin from the molded green body, and machining the degreased body before or after the final firing. However, this method has drawbacks in that the degreased molded body is liable to have a crack therein or deformation thereof owing to different degreasing rates at different thickness portions of the body in the degreasing process so that the yield of product is considerably low, and that the chips produced by machining the degreased body can never be reused owing to the disappearance of the molding additive so that the production cost is extremely expensive.